Research will be conducted into optical fiber-coupled fluorescent sensors for the continuous in vivo monitoring of blood gases. The purpose of phase I is to identify fluorescent chemical systems specifically sensitive to pH, pO2, pCO2, and temperature. From these identified systems, a selection will be made of those compatible for use in a mixed sensor probe. The goal of this study is to minimize the number of separate fibers required to meet the need for a low cost blood gas sensing radial artery catheter. This study has implications in both improving the quality of intensive care for critically ill patients while simultaneously reducing costs through reduction in the number of clinical laboratory test samples required during the course of treatment. It is estimated that a commercial market for fully-sensed radial artery catheters costing under $65 will approach 1/4 million units within five years of its introduction.